Measurements of blood pressure and anthropometric measurements of length, weight, waist circumference and bone densitometry (DEXA) and body composition (fat mass% and fat free mass) using a Air Displacement Plethysmography ( BOD POD) Questions about diet, vitamin supplements, foreign travel, how much time the children spend time outdoors and the use of sunscreen as well as questions about the child's health and family situation will be answered by the parents through a questionnaire. To investigate the possible association between vitamin D status and mental well-being, the investigators will use the Child Behaviour Checklist (CBCL).